A blend of polycarbonate and vinyl copolymer should have good flame retardancy, high heat resistance and high mechanical strength because the blend is applied to heat-emitting products such as electric or electronic goods and office supplies.
To provide the blend with good flame retardancy, a halogen-containing flame retardant and/or an antimony-containing compound were used. However, the disadvantage could be observed that the halogen-containing compound is fatally harmful due to the toxic gases liberated in case of fire. Therefore, flame retardants which are prepared without a halogen-containing compound have become a major concern in this field.
It is commonly a known method to apply a phosphorus ester compound as halogen-free flame retardant to a resin composition. U.S. Pat. Nos. 4,692,488 and 5,061,745 disclose a thermoplastic resin composition comprising aromatic polycarbonate, acrylonitrile-butadiene-styrene graft copolymer, thermoplastic copolymer and monomeric phosphoric acid ester compound as flame retardant. However, the resin composition using the monomeric phosphoric acid ester compound as a flame retardant has very poor heat resistance and shows a juicing phenomenon which occurs during molding process because the flame retardant agent form the laminate on the surface due to the volatility.
As a method for overcoming the juicing problems, the method increasing the molecular weight of phosphoric acid ester is commonly used. And, as a method for increasing the molecular weight of phosphoric acid ester, the introduction of substitute group to a monomeric phosphoric acid ester compound or the use of an oligomeric phosphoric ester compound is proposed. U.S. Pat. No. 5,206,404 discloses a composition having stability against acid and hydrolysis by use of alkyl substituted aryl phosphoric ester compound. Japanese Patent Application Laid Open No. 59-202,240 discloses a process of preparing an oligomeric phosphate and the use of the oligomeric phosphate in a polyamide or polycarbonate resin composition. U.S. Pat. No. 5,204,394 also discloses a flame retardant resin composition comprising an aromatic polycarbonate resin, a styrene-containing copolymer or a graft copolymer, and oligomeric phosphate as flame retardant. Although the resin composition improves the juicing phenomenon and heat resistance, but is inferior to the resin composition using the monophosphorous esters as flame retardants in flame retardancy. Accordingly, to maintain good flame retardancy, the resin composition should contain more flame retardants than in the resin composition containing the monophosphorous esters as flame retardants.
U.S. Pat. No. 5,672,645 describes flame retardant PC/ABS resin composition whose stress cracking resistance is improved by using a combination of a monomeric phosphorus compound and an oligomeric phosphorus compound derived from bisphenol-A, resorcinol or hydroquinone. However, deterioration of heat resistance and juicing phenomenon are still observed due to the monophosphorous compound. And, as the flame retardation ability of an oligomeric phosphate ester is less than that of a monophosphorous ester in usual, the more oligomeric phosphate ester is contained in the flame retardant agent, the poorer flame retardancy of resin composition is.
The present inventors have developed a flame retardant thermoplastic resin composition that comprises a polycarbonate resin, a rubber modified vinyl graft copolymer, a vinyl copolymer, a monomeric phosphoric acid ester compound, an oligomeric phosphoric acid ester and a fluorinated polyolefin resin, which has a good balance of physical properties such as flame retardancy, impact strength, heat resistance, thermal stability, processability and appearance.